Projection display systems based on phase modulators are under development as alternatives to displays based on amplitude modulators. For example, when a liquid crystal on silicon (LCOS) phase modulator is programmed with a kinoform, the corresponding real image is obtained by illuminating the modulator with a laser.
Displays based on phase modulators have better optical efficiency than those using amplitude modulators such as conventional liquid crystals, digital mirror devices or MEMS light valves. A phase modulator steers input light to a projection screen while an amplitude modulator discards light to create dark states. Typical video content is only about 25% as bright as the maximum brightness state; e.g. an all white image. A display system using a phase modulator for video therefore requires only one quarter the optical input power of a corresponding system using an amplitude modulator.
Compared to amplitude modulators, phase modulators are also more tolerant to pixel failures, lens aberrations and variations in beam quality from light sources. However, two-dimensional phase modulators for video depend on high-speed computing to calculate their input signals. Their success in video projection “is directly linked to the availability of fast two-dimensional FFT processors,” according to Georgiou et al. (Journal of Optics A: Pure and Applied Optics 10 (2008) 035302). Phase modulators may also generate unwanted image artifacts if they are unable to create all phases from zero through 2π.
A one-dimensional phase modulator for a light steering optical switch was described by Bloom and Godil (U.S. Pat. No. 6,268,952) as a way to “emulate a continuous mirror tilted by using discrete reflective segments.” Their phase modulator couples light from fiber optic inputs to fiber optic outputs. The light steering optical switch takes advantage of reflective MEMS ribbon technology which can produce switching speeds as fast as 20 nanoseconds.
Despite conventional thinking that a two-dimensional phase modulator is required to create a two-dimensional image, what is needed is a display system based on a one-dimensional phase modulator. Such a system should make use of the high switching speeds available with some optical MEMS to provide an escape from the limitations of current two-dimensional phase modulator based display systems while retaining their robustness and optical efficiency.